c++|string模拟实现

一、string.h

二、string.cpp

三、Test.cpp

对string的各种接口进行一个简易版的模拟实现，在模拟实现完之后对string的底层实现有了进一步的理解，了解大佬的编程写法思路。也算是对string有了一个小总结。

一、string.h

接口的声明。放在.h文件中

#include <iostream>
#include <string>
#include <assert.h>
using namespace std;namespace bit
{class string{public:typedef char* iterator;//迭代器本质上就是指针typedef const char* const_iterator;iterator begin() const{return _str;}iterator end(){return _str + _size;}const_iterator end() const{return _str + _size;}string(const char* s = "");string(const string& s);string& operator=(string s);~string();void push_back(char c);string& operator+=(char c);string& operator+=(const string& s);string& operator+=(const char* str);void append(const char* str);void clear();void swap(string& s);const char* c_str()const;//capacitysize_t size();size_t capacity();void resize(size_t n, char c = '\0');void reserve(size_t n);bool empty()const;bool operator<(const string& s);bool operator<=(const string& s);bool operator>(const string& s);bool operator>=(const string& s);bool operator==(const string& s);;bool operator!=(const string& s);char& operator[](size_t i);const char& operator[](size_t i) const;//返回字符第一次在字符串出现的位置size_t find(char c, size_t pos = 0) const;;//在pos位置插入字符cstring& insert(size_t pos, char c);//在pos位置插入字符串string& insert(size_t pos, const char* str);//返回子串在字符串中出现的位置size_t find(const char* str, size_t pos = 0);string substr(size_t pos = 0, size_t len = npos);//	删除pos位置上的元素，并返回该元素的下一个位置string& erase(size_t pos, size_t len = npos);private:size_t _size;size_t _capacity;char* _str;//静态变量可以赋值处理的前提是有const修饰，这个可以看作是编译器的特殊处理，只能适用于整形家族static const size_t npos = -1;};ostream& operator<<(ostream& out, const string& s);istream& operator>>(istream& in, string& s);
}

二、string.cpp

接口的各种实现。进行声明定义分离时，要注意格式上的变化，指定类域，声明和定义中，只有声明中可以给缺省值，定义中不能给。string的构造函数有传统写法和现代写法，现代写法更简洁，但和传统写法本质上没有太大的区别

#include "string.h"namespace bit
{//string()//	:_str(nullptr)//不能给空，析构时会对空指针解引用，从而报错//	,_size(0)//	,_capacity(0)//{}//string()//	:_size(0)//	,_capacity(_size)//	,_str(new char[_capacity + 1])//这样必须给定成员变量声明顺序。//{}string::string(const char* s){_size = strlen(s);_capacity = _size;_str = new char[_capacity + 1];strcpy(_str, s);}//传统写法/*	string(const string& s){_str = new char[s._capacity + 1];_size = s._size;_capacity = s._capacity;strcpy(_str, s._str);}*///现代写法string::string(const string& s){string tmp(s._str);swap(tmp);}//传统写法//string& operator=(const string& s)//{//	if (*this != s)//	{//		char* tmp = new char[s._capacity + 1];//		delete[] _str;//		strcpy(tmp, s._str);//		_str = tmp;//		_size = s._size;//		_capacity = s._capacity;//		return *this;//	}//	return *this;//	//}//现代写法/*string& operator=(const string s){string tmp(s._str);swap(tmp);return *this;}*/string& string::operator=(string s){swap(s);return *this;}string::~string(){delete[] _str;_str = nullptr;_size = 0;_capacity = 0;}//modifyvoid string::push_back(char c){if (_size == _capacity)//初始化容量以及判断容量是否满了{size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;/*		if (_str != ""){char* tmp = new char[newcapacity + 1];memcpy(tmp, _str, _size);delete[] _str;_str = tmp;_capacity = newcapacity;}*/reserve(newcapacity);}_str[_size] = c;_size++;_str[_size] = '\0';}string& string::operator+=(char c){push_back(c);return *this;}string& string::operator+=(const string& s){if (_size + s._size > _capacity){reserve(_size + s._size);}strcpy(_str + _size, s._str);_size += s._size;return *this;}string& string::operator+=(const char* str){append(str);return *this;}void string::append(const char* str){if (_size + strlen(str) > _capacity){reserve(_size + strlen(str));}strcpy(_str + _size, str);_size += strlen(str);}void string::clear(){_str[0] = '\0';_size = 0;_capacity = 0;}void string::swap(string& s){std::swap(_str, s._str);std::swap(this->_size, s._size);std::swap(this->_capacity, s._capacity);}const char* string::c_str()const{return _str;}//capacitysize_t string::size(){return _size;}size_t string::capacity(){return _capacity;}void string::resize(size_t n, char c){if (n > _capacity){reserve(n);for (int i = _capacity; i < n; i++)push_back(c);}else if (n > _size && n < _capacity){for (int i = _size; i < n; i++)push_back(c);}else if (n < _size){_str[n] = '\0';}}void string::reserve(size_t n){if (n > _capacity){char* tmp = new char[n + 1];strcpy(tmp, _str);delete[] _str;_str = tmp;//_size = strlen(tmp);_capacity = n;}}bool string::empty()const{return _str == "";}bool string::operator<(const string& s){return strcmp(_str, s._str) < 0;}bool string::operator<=(const string& s){return !(*this > s);}bool string::operator>(const string& s){return strcmp(_str, s._str) > 0;}bool string::operator>=(const string& s){return !(*this < s);}bool string::operator==(const string& s){return strcmp(_str, s._str) == 0;}bool string::operator!=(const string& s){return !(strcmp(_str, s._str) == 0);}char& string::operator[](size_t i){return _str[i];}const char& string::operator[](size_t i) const{return _str[i];}//返回字符第一次在字符串出现的位置size_t string::find(char c, size_t pos) const{assert(pos <= _size);for (int i = pos; i < _size; i++){if (_str[i] == c)return i;}return npos;}//在pos位置插入字符cstring& string::insert(size_t pos, char c){assert(pos <= _size);if (_size == _capacity){size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;reserve(newcapacity);}if (pos == _size)push_back(c);else{size_t len = _size - pos;while (len){_str[pos + len] = _str[pos + len - 1];len--;}_str[pos] = c;}_size++;_str[_size] = '\0';return *this;}//在pos位置插入字符串string& string::insert(size_t pos, const char* str){assert(pos <= _size);size_t len = strlen(str);if (len + _size >= _capacity){reserve(len + _size);}if (pos == _size){append(str);}else{size_t ilen = _size - pos;while (ilen){_str[pos + ilen + len] = _str[pos + ilen];ilen--;}for (int i = pos, j = 0; i < pos + len; i++, j++){_str[i] = str[j];}}_size += len;_str[_size] = '\0';return *this;}//返回子串在字符串中出现的位置size_t string::find(const char* str, size_t pos){assert(pos <= _size);size_t len = strlen(str);if (pos + len > _size)return npos;else{size_t fpos = find(str[0], pos);for (int i = fpos, j = 0; i < fpos + len; i++, j++){if (str[j] != _str[i])return npos;}return fpos;}}string string::substr(size_t pos, size_t len){assert(pos <= _size);string tmp;size_t end = pos + len;//if (len == npos || len >= _size - pos)//{//	tmp.reserve(_size - pos);//	strcpy(tmp._str, _str + pos);//	return tmp;//}//else//{//	memcpy(tmp._str, _str + pos, len);//	tmp[len] = '\0';//	return tmp;//}if (len == npos || len >= _size - pos){end = _size;}tmp.reserve(end - pos);for (int i = pos; i < end; i++){tmp += _str[i];}return tmp;}//	删除pos位置上的元素，并返回该元素的下一个位置string& string::erase(size_t pos, size_t len){assert(pos < _size);if (len == npos || len > _size){_str[pos] = '\0';}else{/*size_t length = len + pos;while (pos < length){_str[pos] = _str[pos + len];pos++;}_str[_size - len] = '\0';*/strcpy(_str + pos, _str + pos + len);_size -= len;}return *this;}ostream& operator<<(ostream& out, const string& s){for (auto e : s){out << e;}return out;}istream& operator>>(istream& in, string& s){s.clear();char buff[128];char ch = in.get();int i = 0;while (ch != ' ' && ch != '\n'){buff[i] = ch;i++;if (i == 127){buff[i] = '\0';s += buff;i = 0;}ch = in.get();}if (i > 0){buff[i] = '\0';s += buff;}return in;}}

三、Test.cpp

测试版本，对接口进行测试，写了三个测试版本，但并没有调用全部接口，进行一番演示，大致还行，可能还有错误，也是水平有限。

#include "string.h"
namespace bit
{void stringtest1(){string s("hello world");string::iterator it = s.begin();while (it != s.end()){cout << *it;it++;}cout << endl;for (auto e : s){cout << e;}cout << endl;string s1(s);string s2 = s1;for (auto e : s1){cout << e;}cout << endl;for (auto e : s2){cout << e;}cout << endl;}void stringtest2(){string s("hello world");s += "hello world";for (auto e : s){cout << e;}cout << endl;string s1;s1.push_back('a');s1.push_back('b');s1.push_back('c');s1.push_back('d');for (auto e : s1){cout << e;}cout << endl;cout << (s < s1);cout << (s > s1);cout << (s == s1);cout << (s <= s1);cout << (s >= s1);cout << true;};void stringtest3(){string s("hello world");string s1 = "excuse me";/*s.swap(s1);cout << s.c_str() << " " << s1.c_str() << endl;cout << s.capacity() << endl;s.reserve(100);cout << s.capacity() << endl;s.resize(5);cout << s.capacity() << " " << s.c_str() << endl;;*///cout << s[0];size_t pos = s.find("world");cout << pos << endl;cout << s.substr().c_str() << endl;s.insert(0, 'w');cout << s.c_str() << endl;s.insert(6, 'e');cout << s.c_str() << endl;s1.insert(0, "hello");cout << s1.c_str() << endl;s1.insert(5, "hello");cout << s1.c_str() << endl;cin >> s1;cout << s1;}
}
int main()
{bit::stringtest1();bit::stringtest2();bit::stringtest3();return 0;
}

三个测试函数的输出结果：